"Based on a growing body of preliminary research, there is scientific consensus that Zika virus is a cause of microcephaly and Guillain-Barre syndrome," the World Health Organization said in its weekly Zika virus situation report Thursday.

The agency said research continues to determine a "causal link" between the Zika virus and neurological disorders in fetuses, newborns, infants and adults. This includes trying to quantify what the risk is for pregnant women and others.

Since last year the virus has infected hundreds of thousands of people in nearly 60 countries. Symptoms include a rash, fever, joint pain and red eyes (conjunctivitis). However, 80%of those infected have no symptoms. The virus is primarily transmitted via infected Aedes aegypti mosquitoes, but it is also sexually transmitted.

Join the conversation

See the latest news and share your comments with CNN Health on Facebook and Twitter.

In February the WHO declared a public health emergency of international concern over the virus. This was prompted largely by how fast the outbreak was spreading and because of the link -- just suspected, at that time -- to microcephaly and other possible neurological defects. The agency predicts 3 to 4 million people will be infected within a year.